1. Field of the Invention
The present invention relates to positron emission tomography (PET). More particularly, the present invention relates to PET detectors used therein.
2. Description of Related Art
The use of positron emissions for medical imaging has been well documented from the early 1950s, see “A History of Positron Imagining,” Brownell, Gordon, presented on Oct. 15, 1999, Massachusetts General Hospital and available at http://neurosurgery.mgh.harvard.edu/docs/PEThistory.pdf, which is incorporated herein by reference in its entirety. PET imaging has advantages over other types of imaging procedures. Generally, PET scanning provides a procedure for imaging the chemical functionality of bodily organs rather than imaging only their physical structure, as is commonly available with other types of imaging procedures such as X-ray, Computerized Tomography (CT), or Magnetic resonance imaging (MRI). PET scanned images allow a physician to examine the functionality of the heart, brain, and other organs, as well as diagnosing disease groups which cause changes in the cells of a body organ or in the manner in which they grow, change, and/or multiply out of control, such as cancers.
Positron Emission Tomography (PET) is a medical imaging technique that involves injecting a natural compound, such as sugar or water, labeled with a radioactive isotope into a patient's body to reveal internal biological processes. As the isotope (positron) circulates within the patient's body. The positron annihilates with an electron and emits pairs of photons in diametrically opposed directions (back-to-back). A PET device is made of a set of detectors coupled to thousands of sensors that surround the human body. These detectors (crystals) capture the photons emitted by the isotope from within the patient's body at a total rate of up to hundreds of millions per second, while the sensors (transducers such as PMTs) convert them to electrical signals, and send the signals to the electronics.
Other applications for detecting particles (photons, electrons, hadron, muon and jets) are well known, such as with regard to experiments in high energy physics. While particle detection in high energy physics and medical imaging have some common ground, differences between the disciplines are sticking. One distinction between the usages is that the detectors used in medical imaging are approximately 200 times smaller than the larger detectors employed in high-energy physics applications, and what is more, medical imaging PET applications require the identification of only a single type of particle, the photon.
Typically, prior art Positron Emission Tomography (PET) devices require the injection into the patient's body of a radiation dose that is 10 to 20 times the maximum radiation dose recommended by the International Commission on Radiological Protection (ICRP). This amount is necessary because, at best, prior art PET devices detect only two photons out of 10,000 emitted in the patients' body. Currently, the largest manufacturers of PET (General Electric Company and Siemens AG (ADR)) which command in excess of 90% of the world market, are manufacturing two different PET (PET/CT) systems with very similar performance and are selling them at very similar prices. However, although the price and performance of the systems from the different manufacturers are comparable, one manufacturer's system (Siemens) uses nearly ideal crystal detectors, while contrastingly, the other manufacturer's system (General Electric) uses cheaper, lower quality crystal detectors with slower decay time. Consequently, the manufacturer using the cheaper, lower cost detectors, expends on the order of only 10% the price of the ideal crystals used in their competitor's systems. Thus, the question arises as to how it could be that, even though one manufacturer uses crystal detectors that are ten times more expensive that the other manufacturer, the price and performance of the two PET systems from the different manufacturers are very comparable.
Anecdotally, the present inventor has analyzed the progress of the most significant PET improvements made in the most recent 17 years, see “400+ times improved PET efficiency for lower-dose radiation, lower-cost cancer screening,” 3D-Computing, Jun. 30, 20010, ISBN: 0970289707, which is incorporated herein by reference in its entirety. During that time period, the efficiency of PET improved at a rate of between two and three times every five years. The analysis included technical literature, patents (including those assigned to GE and Siemens) and also PETs that were built as prototypes at several universities but were never commercialized. At the current improvement rate of PET advancement, it would conservatively take several decades of improvements for the radiation dose necessary for a PET procedure to come within the maximum radiation dose recommended by the ICRP.
What is needed is a means for increasing the accuracy and efficiencies of PET devices enabling caregivers to more accurately diagnose aliments related to the functionality of body organs and not just inferences from the structure of the organs. Additionally, what is needed is a quantum advance forward in PET devices and procedures wherein patients can receive the benefits of PET imaging without the associative risks from the radioactive doses necessary for the procedures. Finally, what is needed is a means for reducing the associated risks and increasing detection efficiencies associated with PET imaging procedures to such an extent that the benefits of PET imaging can be applied in well-body care and preventative medicine strategies for apparently healthy individuals as a standard health assessment and diagnostic tool for regular, periodic checkups.